Plastic pelletizers



June 6, 1967 J. 1.. SWICKARD, JR, ETAL 3,323,170

PLASTIC PELLETIZERS Original Filed June 1, 1965 2 Sheets-Sheet I FIG-I II We 74 1 I| MT IA \W I I I I8 I II 65 77o a! 94 80 4 I 1NVENTOR$ JAMESa... swmwmn m a 90 BY HARVEY H. GOVEI June 1967 J. 1.. SWICKARD, JR,ETAL 3,323,170

PLASTIC PELLETI ZERS 2 Sheets-Sheet Original Filed June 1, 1965 mwwmvsUnited States Patent 3,323,170 LASTEC PELLETIZERS James L. Swickard,lira, and Harvey H. Gove, both of Hamilton, Ohio, assignors to The BlackClawson Company, Hamiiton, Ohio, a corporation of fihio Originalapplication June 1, 1965, Ser. No. 460,116, new Patent No. 3,287,764,dated Nov. 29, 1966. Divided and this application Nov. 22, 1966, Ser.No. 596,173

5 Claims. (6!. 18--12) This invention relates to plastic pelletizers,and more particularly, to an improved die plate for a plasticpelletizer. This application is a division of application Ser. No.460,116, filed June 1, 1965, now Patent No. 3,287,764.

It has been found desirable to heat the die plate in a plasticpelletizer to assure that the plastic material or polymer which isextruded through orifices formed in the die plate does not cool andsolidify before the material is discharged. Also the die is heated whenstarting up to melt or soften the remaining polymer which hardened inthe orifices after a previous shut down. Commonly, the orifices formedin the die plate are arranged in an annular pattern with the orificesspaced close together so that a maximum number of pellets can beproduced by a die plate of predetermined size. For heating the dieplate, usually a fluid such as steam, hot oil or other heat transferfluids is directed through the die plate in close proximity to theorifices so that the fluid effectively heats the surfaces defining theorifices.

A knife member is commonly rotatably mounted adjacent the die plate andis provided with a cutting knife which rotates in contact with the dieplate and sweeps the discharge end of the orifices to shear the extrudedstrings of plastic material into small bits which are solidified intopellets by a flow or spray of cooling fluid such as Water. The wateralso serves to carry the pellets away .from the die plate for subsequentdrying and packaging.

To prevent the fluid employed for cooling the pellets from also coolingthe die plate, it has been found desirable to expose only a nozzleportion of each orifice sufficient t0 define a cutting surface for theknife and then surround these nozzle portions with a suitableinsulation. This construction is shown in the copending application ofRobert E. Hoffman and H. Paul Koppehele, Ser. No. 261,382, filed Feb.27, 1963, now Patent No. 3,230,582 and assigned to the same assignee asthe present invention.

To provide an effective and clean shearing action of the extrudedstrings of plastic material, the rotary cutting knives are preferablymounted on an inclined angle in relation to the cutting surface definedby the nozzle portions and tangential to the hub supporting the cuttingknives. As a result of this position of the cutting knives and of thesmall diameter of the nozzle portions, it has been found uneconomical inproduction to control the precise position of the cutting knives toprevent them from extending beyond the inner and outer annular rows ofnozzle portions.

Thus after an extended period of use, it has been found that the endportions of the cutting knives which do not contact the cutting surfacedefined by the nozzle portions will wear substantially less than thecenter portion of the knife. This uneven wear of the cutting knives hasbeen found to result in a corresponding non-uniform Wear of the dieplate and eventually prevents a clean shear of the pellets and alsocauses the knife to form grooves in the insulation material.

It is also desirable to construct a die plate for a plastic pelletizerso that a heating liquid flows uniformly through the die plate wherebyall of the orifices are maintained at a substantially uniformtemperature and thus the plas- Patented June 6, 1967 tie materialextruded through the orifice will be maintained at a uniform temperatureand the pellets will be formed of uniform size. Thus it has been founddesirable to provide a zig-zag or serpentine-like flow path for theheating liquid around the orifice so that each orifice is uniformlyheated and the liquid cannot short circuit or bypass some of theorifices. This serpentine-like arrangement is especially desirable for aliquid heating fluid such as hot oil which has a greater tendency toflow along the path of least resistance than does a gaseous fluid suchas steam.

It has also been found that a die plate made up of interfitting annularpieces offers particular advantages, by decreasing the cost ofconstruction and by increasing reliability over other known types ofpelletizer die plates. The machining steps for forming the heatingpassageways to provide a distinct serpentine-like flow can thus beformed in one or more of the die plate sections prior to assembly.Preferably, a center or intermediate section contains a major portion ofthe heating passageways as well as the passageway return orinterconnecting conduits, thereby confining a major portion of themachining of the intermediate section.

Accordingly, it is a primary object of the present invention to providean improved die plate of simplified construction wherein a highconcentration of orifices are heated uniformly by a heating fluid whichflows in close proximity to each of the orifices and cannot bypass anysection or group of orifices.

It is also an object to provide a die plate as outlined above whereinthe heating fluid, preferably a liquid is positively directed throughthe die within passageways which are connected together to provide adistinct serpentine-like flow path so that the die is heated evenly anduniformly, and the construction is such that substantial internalpressure are withstood Without short circuiting the heating flow pathshould it be necessary to increase fluid pressure to purge or clean theheating passageway.

A further object of the invention is to provide an improved die plate asoutlined above, which is constructed in three sections so that thepassageways for the heating fluid can be easily formed and connected toprovide a distinct serpentinedike flow path for the heating fluidthrough the die plate.

Still another object of the invention is to provide an improved plasticpelletizer which includes a die plate and a knife member rotatablymounted adjacent the die plate and wherein the die plate is providedwith hardened nozzle portions and wear stubs to provide a uniform wearalong the knife member and to minimize wear of the die plate so thatthese components are provided with a long service life.

A more specific object of the invention is to provide an improved dieplate for a plastic pelletizer as outlined above, wherein the die plateincludes a series of carbide nozzle tips for defining a cutting surfaceand further includes a series of corresponding carbide wear stubs whichcooperate with the carbide nozzle tips to provide a uniform wear alongthe cutting edge of the rotating knives and thereby provide forprecision shearing of the plastic into pellets over an extended periodof use.

As another object, the invention provides a die plate construction asoutlined above which can be easily inspected and serviced in case a leakof heating fluid should develop since the only sealed joints Where leakscould possi'bly develop are the exposed welds which join the annular diesections.

It is also an object of the invention to provide an improved die plateas outlined above wherein the orifices through which the plasticmaterial is extruded are arranged in closely spaced radial rows With aplurality of axially spaced passageways extending radially between therows of orifices so that a high capacity of heating fluid can becirculated within the die plate while also providing for a highconcentration of orifices.

Other objects and advantages of the invention will be apparent from thefollowing description, the accompanying drawings and the appendedclaims.

In the drawings FIG. 1 is an axial section view of a plastic pelletizerincluding an improved die plate formed in accordance with the invention;

FIG. 2 is an enlarged axial section view of the die plate shown in FIG.1;

FIG. 3 is an enlarged fragmentary plan view in part section of the dieplate shown in FIG. 2;

FIG. 4 is an enlarged fragmentary section view of a portion of the dieplate showing a series of axially extending orifices as seen along theline 44 of FIG. 3;

FIG. 5 is a fragmentary radial view of the center section of the dieplate as viewed along the line 55 of FIG. 2 and showing the inlet to thepassageways for the heating fluid;

FIG. 6 is a further fragmentary radial view of the die plate centersection viewed along the line 66 of FIG. 2 and showing a typical outerslot for reversing the flow of heating fluid through the passageways;and

FIG. 7 is a still further fragmentary radial view of the die platecenter section as viewed along the line 7-7 of FIG. 2 and showing atypical inner slot for reversing the flow of the heating fluid betweenadjacent passageways.

Referring to the drawings which illustrate a preferred embodiment of theinvention, the plastic pelletizer shown in FIG. 1 includes generally abody 10 which is provided with a flat face 12 for mounting thepelletizer on the barrel of a plastic extruder with the aid of anadaptor, or on a mixing valve or other suitable source of molten plasticmaterial. The molten plastic material or polymer is forced into atransverse inlet passageway 14 formed within the body 10 and into anannular chamber 16 defined by a bore 18 formed within the body 10 andthe cylindrical outer surface 22 of a stationary mandrel 24 mountedwithin the bore 18.

Preferably, the mandrel 24 is provided with an inclined annular ledge orsurface 26 which directs the plastic material axially within the chamber16 towards the annular choke portion 27 formed as an integral part ofthe mandrel 24. The surface 26 and choke portion 27 cooperate to providea uniform distribution or flow of material around the choke portion. Theplastic material then flows into an extrusion chamber 30 which isdefined by the cylindrical surface 22 of the mandrel 24 and afrusto-conical surface 32 formed within the body 10.

Formed within the end of the body 10 is a counterbore 34 in which ismounted a circular die plate 35 which is secured to the body 10 by aseries of screws extending through the openings 36 and to the mandrel 24by a series of screws extending through the openings 37. As shown inFIG. 2, the die plate 35 is formed by welding together three annularsections including an inner section 38, an intermediate or centersection 40 and an outer section 42 so that all of the weld joints areexposed for inspection and repair. These sections are provided withcorresponding annular shoulders or steps 43 and 44 which simplifyprecision assembly of the sections and support the center section 40against pressure exerted by the plastic material.

Formed within the intermediate annular section 40 are a series ofrelatively small diameter axially extending orifices 45 which arearranged in radial rows spaced around the entire annular section 40 asindicated in FIG. 3. Preferably the orifices 45 are provided with aconical-shaped inlet portion 47 which aid in providing a uniform flow ofmaterial into the orifices 45.

As shown in FIG. 4, an annular shallow recess 48 is formed within theintermediate section 40 and a series of cylindrical nozzle tips 50 aremounted within the recess.

The nozzle tips are provided with orifices 52 which serve as extensionsof the orifices 45. Preferably the nozzle tips 50 are formed fromtungsten carbide steel and are secured within the annular recess 48 by asuitable brazing operation. Surrounding the hardened nozzle tips 50 andfilling the remainder of the annular recess 48 is a layer of insulationmaterial 55 (FIG. 2) which preferably is formed from a fiberglass filledsilicon molding compound which is forced under pressure into the recess48 after the nozzle tips 50 are in place to provide a thermal barrier toprevent cooling of the die plate by the pellet entraining water.

Mounted on the end surface 58 (FIG. 1) of the outer section 42 of thedie plate 35 is a housing 60 which defines a water-tight chamber 61. Thehousing 60 is secured to the body 10 for quick removal by a series offour swing bolts 63 and wing nuts 64 which are carried by acorresponding series of support blocks 65 mounted on the body 10 by thescrews 67.

Formed within the inner section 38 of the die plate 35 is an opening 68through which extends a shaft 70 which is rotatably supported bysuitable bearings (not shown) mounted within the stationary mandrel 24as shown in the aforementioned application. The shaft 70 is rotated by amotor 72 through a flexible drive coupling 74 which connects the motorshaft 76 to the shaft 70 within the cylindrical housing 78.

Mounted on the opposite end of the shaft 70 by a threaded or springloaded connection 79 within the housing 60 is a knife member 80 whichcarries a series of knife blades 82. As shown in FIG. 1, and in greaterdetail in the aforementioned application, the knife blades 82 aremounted on the hub 84 in an inclined position relative to the cuttingsurface defined by the end surfaces 56 of the cylindrical nozzle tips50. Preferably, the blades 82 are mounted tangentially on the hub 84 asmentioned above so that the cutting edge 85 of each blade 82 sweeps thecutting surface with a shearing action causing the plastic stringsextruded through the orifices 45 and 52 to be cleanly severed into smallbits. It is most desirable that the strings of plastic be shearedcleanly so that there remain no fine tails connecting successive bits.Thus it is highly desirable to have precision contact between thecutting edge 85 of each knife blade and the cutting surface 56 of eachnozzle tip 50.

The chamber 61 which is defined by the housing 60 is supplied with achilling liquid such as water through the inlet 90. The water isdirected into the chamber 61 through the passages 92 formed within thehub 84 so that the blades 82 are continuously flushed. The water isemployed to cool the bits of plastic material extruded through theorifices 45 and cut by the blades 82 to solidify them to form hardenedpellets and to entrain the same for removal through the outlet 94.

As shown in FIG. 3, the individual nozzles are arranged in annularconcentric paths and radial rows with the adjacent nozzles in each rowbeing arranged in laterally staggered relation to those in the nextnozzle row. In the specific embodiment shown, there are alternate radialrows of four nozzles and five nozzles each, respectively. Therefore,with this arrangement, the radial nozzle rows having only four nozzlesare somewhat shorter in length than the adjacent radial rows which havefive nozzles. The grouping permits the optimum number of nozzles to becontained within the intermediate section 40, so that a maximum numberof pellets can be formed within the available space. However, thearrangement is such that in order for the knife blade 82 to sweep thefull annular extent of the intermediate section 40, it is necessary thatsuch blades have a diagonal length which somewhat exceeds the maximumand minimum radial extent of the nozzles, themselves.

Referring to FIGS. 3 and 4, mounted within a series of cylindricalopenings 98 formed adjacent the inner and outer annular peripheries ofthe recess 48 are a series of wear stubs 100. The stubs are preferablypositioned at the ends of the shorter rows, and are preferably formedfrom the same material as the nozzle tips 50. The wear stubs may thus beformed of tungsten carbide as the tips 50 and serve to extend thecutting surface defined by the end surfaces 56 of cylindrical nozzletips 50 so that the end portions 101 of the knife blades 82 also contacthardened material. In this manner the cutting edge 85 (FIG. 1) of theblades will wear uniformly along the full length of the blades. Thus astthe knife blades sweep around the annular cutting surface defined bythe nozzle tips 50 and the Wear stubs 100, all portions of the cuttingedge 85 engage the carbide material. As a result, the knife blades 82wear evenly and do not form projections which groove the insulationmaterial 55 inserted between the nozzle tips 50.

To provide for a circulation of heating fluid within the intermediatesection 40 of the die plate 35 so that the plastic material does notsolidify within the orifices 45 and 52, a series of radially extendingpassageways 105 (FIG. 3) are formed within the intermediate section 40between the radial rows of orifices 45. As shown in FIG. 5, thepassageways 105 are formed in pairs spaced axially apart and withrelatively small diameters to provide an adequate heat exchange surfaceand volume handling capacity, and so that the rows of orifices 45 can bespaced close together as shown in FIG. 3. The multiple axially spacedpassageways 105 provide for a high flow capacity of the heating fluidthrough the intermediate section 40 which has been found desirable toprovide a quick transfer of heat into the die plate.

The heating fluid, which is usually either steam or hot oil, is suppliedto the passageways 105 by a plurality of inlets 107 formed radiallywithin the outer section 42 as shown in FIGS. 2 and 3. In order for asingle inlet passage 107 to supply a pair of axially spaced passageways105, the outer periphery of the intermediate annular section 40 isprovided with a milled slot 110 which connects the inner end of an inletpassage 107 with the outer ends of a pair of passageways 105 (FIG. 5).

As shown in FIG. 3, the flow of heating fluid through the passageways105 is directed along a radial serpentinelike flow path, as shown by thearrows. This reversing flow path is provided by a series of milled slots115 and 116 which are formed around the inner and outer peripheries ofthe intermediate section 40 so that the corresponding ends of adjacentpairs of passageways 105 are interconnected, as shown in FIGS. 3, 6 and7.

Preferably the die plate 35 is provided with six inlet passages 107 andthree radially extended outlet passages 118 within the outer section 42so that the die plate is divided into six sectors and the heating fluidflows separately along a serpentine-flow path through each sector or 60.Thus as shown in FIG. 3, a separate inlet passage 107 is provided foreach sector of the die plate 35 and one outlet passage 118 serves twoadjacent sectors. By this construction, the heating fluid flows into thedie plate through inlet passages spaces 120 apart and is dischargedthrough outlet passages also spaced 120 apart. As a result, each of theorifices 45 are heated to substantially the same temperature.

It can be seen from the drawings and the above description that a dieplate constructed in accordance with the present invention providesseveral desirable features and advantages. By forming the die plate inthree annular sections with the intermediate section 40 provided withthe radial flow passageways 105 and the outer section 42 provided withthe inlet and outlet passages 107 and 118 respectively, the constructionof the heated die plate has been substantially simplified.

The slots 110, 115 and 116, direct the heating fluid through the dieplate along a uniform serpentine-like flow path so that all of theorifices 45 are heated. In addition, by dividing the die plate into aplurality of six sectors with heating fluid circulated separatelythrough each sector, all of the orifices 45 can be maintained atsubstantially a uniform temperature. In the preferred embodiment, theheating passageways and the slots 110, and 116 are confined to thecentral or intermediate die section 40, and thus may be convenientlydrilled into this section prior to assembly and welding with the innersection 38 and the outer section 42. In this manner, a leak-proofheating die plate is assured.

The arrangement of the die plate is such that a maximum amount of heatcan be applied to the die plate and is uniformly distributed to each ofthe nozzles. This is of particular advantage in pelletizing certainpolymers which are critical to temperature, and assures that pellets ofuniform size are at each of the nozzles. Sufficient heat can be appliedto the die plate by this arrangement to permit cold start-ups followingshut down even with water on the face surface of the die plate.

The construction of the die plate is such that leaks can easily bedetected since there is nofluid seal which is covered by insulation.Also, leaks if they should occur, can be repaired without the removal ofany insulation, and any leakage will be confined to one of the foursurface welds joining the intermediate section to the inner and outersections.

Should there become any tendency for the passageways 105 to becomeblocked, such as with burnt oil or the like, a purging fluid under asufficiently high pressure can be applied directly to the inlets 107, orreverse flushed through the outlet 118, as desired, to clean out theheating passageways. The arrangement of the parts is such that highfluid pressure may be used without risking damage to the die plate, dueto the absence of brazed connections in the die plate heating system.

Another feature is provided by forming the radially extendingpassageways 105 in pairs between adjacent rows of orifices 45 to providefor a high flow capacity for heating fluid while obtaining a highconcentration of orifices 45 to provide for a maximum production ofpellets. Also, by combining the carbide wear tubes 100 with the carbidenozzle tips 50, the knife blades 82 and die plate are each provided witha substantially longer service life which has been found to reduce theoperating costs for the plastic pelletizer by a significant margin.

While the form of apparatus herein described constitutes a preferredembodiment of the invention, it is to be understood that the inventionis not limited to this precise form of apparatus, and that changes maybe made therein without departing from the scope of the invention whichis defined in the appended claims.

What is claimed is:

1. An improved extrusion die plate adapted to be mounted on a plasticpelletizer in contact with a rotary knife blade, comprising meansdefining a plate member having a plurality of spaced, generally parallelorifices extending therethrough and arranged in an annular pattern oforifices, a corresponding plurality of discrete nozzle tips secured tosaid plate member in axial alignment with said orifices and forming thedischarge ends of said orifices, said tips having a hardness greaterthan the hardness of said plate member and including correspondingcoplanar outer end surfaces which cooperatively form a cutting surface,a series of wear stubs each having a hardness substantially the same asthat of said tips and mounted on said plate member in spaced relationwith said nozzle tips, and each said stub having a wear surface coplanarwith said cutting surface and cooperating therewith to eflect uniformwear of the knife blade and thereby to minimize grooving of said dieplate.

2. A die plate as defined in claim 1 including means defining anannnular recess within said plate member, said nozzle tips and saidstubs being mounted within said recess in spaced apart relationship toeach other and insulation material substantially filling all spaceswithin said recess between said nozzle tips and said stubs to minimizeheat transfer from said plate member.

3. A die plate as defined in claim 1 wherein said orifices and nozzletips are arranged in a plurality of generally radially extending rows,said orifices and tips in adjacent said rows being radially staggered toprovide spaces radially outwardly and inwardly of certain of said rows,and there being one of said wear stubs positioned in each of saidspaces.

4. A die plate as defined in claim 1 wherein certain of said Wear stubsare spaced radially outwardly beyond the radially outermost ones of saidnozzle tips, and others of said wear stubs are located radially inwardlyof the radially innermost ones of said nozzle tips.

5. A die plate as defined in claim 1 wherein said wear stubs comprise afirst annular series of stubs positioned a radially outwardly of saidtips and a second annular series of stubs positioned radially inwardlyof said tips.

References Cited UNITED STATES PATENTS 2,391,050 12/1945 Horn.

3,114,169 12/1963 Palmer et al 18-12 3,230,582 1/1966 Hoffman et al.1812 3,271,822 9/1966 Rhino 1812 10 WILLIAM J. STEPHENSON, PrimaryExaminer.

1. AN IMPROVED EXTRUSION DIE PLATE ADAPTED TO BE MOUNTED ON A PLASTICPELLETIZER IN CONTACT WITH A ROTARY KNIFE BLADE, COMPRISING MEANSDEFINING A PLATE MEMBER HAVING A PLURALITY OF SPACED, GENERALLY PARALLELORIFICES EXTENDING THERETHROUGH AND ARRANGED IN AN ANNULAR PATTERN OFORIFICES, A CORRESPONDING PLURALITY OF DISCRETE NOZZLE TIPS SECURED TOSAID PLATE MEMBER IN AXIAL ALIGNMENT WITH SAID ORIFICES AND FORMING THEDISCHARGE ENDS OF SAID ORIFICES, SAID TIPS HAVING A HARDNESS GREATERTHAN THE HARDNESS OF SAID PLATE MEMBER AND INCLUDING CORRESPONDINGCOPLANAAR OUTER END SURFACES WHICH COOPERATIVELY FORM A CUTTING SURFACE,A SERIES OF WEAR STUBS EACH HAVING A HARDNESS SUBSTANTIALLY THE SAME ASTHAT OF SAID TIPS AND MOUNTED ON SAID PLATE MEMBER IN SPACED RELATIONWITH SAID NOZZLE TIPS, AND EACH SAID STUB HAVING A WEAR SURFCE COPLANARWITH SAID CUTTING SURFACE AND COOPERATING THEREWITH TO EFFECT UNIFORMWEAR OF THE KNIFE BLADE AND THEREBY TOMINIMIZE GROOVING OF SAID DIEPLATE.